Automatic device for induction-motors.



No. 850,205. I PATENTED APR. 16, 1907. S. R. BERGMAN.

AUTOMATIC DEVICE FOR INDUCTION MOTURS. APPLICATION IILED MAR. 20. 1906.

2 SHEETS-SHEET 1.

Atty,

Nb 850,205. PATENTED APR. 16, 1907.

S. R. BERGMAN.

AUTOMATIC DEVICE FOR INDUCTION MOTORS. APPLIOATION FILED MAR. 20. 1906.

2 SHEETS-SHEET 2.

, lllllllllll f UNITED smi e SVEN PATENT OFFICE. Y

ELECTRIC COMPANY,- A CORPORATION OF-NEW YORK. AUTOMATIC oEvioE FOR INDUCTlON-MOTO'RS.

} Patented April 16,1907.

pplication filed March 20,1906; Serial. NQ- 307,019.

Lynn, county of Essex, State of Massachu-' setts, have invented certain new and useful Improvements in Automatic Devices for In-., duction-Motors, of which the following is a specification. My invention relates 'to single-phase induction-motors of the type having different connections for starting and for running. I-ts means forautomatically making the roper object is to provide efiicient and reliable change from starting'to running con itions when the motor is up to speed.

Since single-phase motors without start ing devices of some sort possess no starting torque, starting-windings or phase-splittin devices, or both are ordinarily employed wit such motors. These starting devices are ornot designed to carry current for any considerable length of time, and consequently must be cut out of circuit when the motor is up to speed. 7 If this operaton'is left to the attendant, the startingdevices may be left in circuit because of carelessness. more, if the devices are cutout of circuit and the volta e fails, so that the motor comes to rest and the current is again thrown onto the motor, the motor will not start and may be seriously damaged by the heavy current which will flow. For these reasons it is exceedin 1y desirable to employ a reliable automatic fievice for cutting out the starting de-' vice when the motor is up tospeed, For this purpose I utilize the change in the shape of the motor-field as the-motor speeds up Although at starting a cross field exists in.

the motor in quadrature with the main field,

due to the'starting devices, this cross-field is much weaker than the main field of the'mo tor, so that the sha of the field is elliptical. As the motor spee s up the current induced in the secondary winding stren hens the.

crossfield, as is well understood in the art,

across the source of current willbe the seat of an induced electromotive force having a eomponent in quadrature with the impressed electromotive force, vwhich will increase as Further- 4 I the motor speeds up, on account oftheincrease of the cross-field. For instance, in a phase not connected to the source increases as the motor s eed increases. -I utilize this matic controlling means arranged in accord: ance with my invent on. Fig. 2 is adiagram ing. Fig. 3 shows a modification of the conm connections.

Figs; 1 and 2, A, A, and A represent the three phases of the winding of a singlephase induction-motor, B represents the secondary member, which may be of the short circuited s uirrel cage type." The three phases of t e primary Winding are shown connected'in'Y, the terminals A and A being connected to the source of current phase A is connected through the contacts 0 to the phase-splitting starting device formed .by the resistance 'R'and inductance I. .The contacts 0 are connected to each other at which is controlled by a magnet D; This magnet is'connected' in shunt to the phase A of the primary winding. The pivoted con- 1 tact C is rovided with an adjustable counterweight arranged to return the contact to closed positionwhen the magnet D is deenergized.- 7

Theo eration is asfollows: At starting the weak, so that the induced electromotive energized to shift t e contact member 0. The motor is consequentl connected for starting withthe phase-sp itting devices in circuit, as shown m 2; As the motor speed rises the cross-field is increased bythe currents induced in the rotor, this cross-field of the primary circuit connections at start cross-fie din the motor is comparativelyforce in the phase A is comparatively smalL; Consequently'the m "net D 1S not sufficiently being in quadrature to the main. motor-field BERGMAN, or LYNN,;MAssAoHus r-'rs, ASSIGNOR To GENERAL single-phase induction-motor having a three-, phase Wmding the electromotive force in the J increase in ucedelectromotive force to o crate a switch for breaking the circuit of phase nduction-motor provided with auto- My invention will best be understood by i v nections of the motor and controlling means, 1 and Fig. 4 is a diagram of the modified start-' through the main switch S. The third startin by a pivoted contact member 0,

both in space and in time, and as the motor I shown, but aim in the appended claims to speed increases the shape of the field more and more nearly approaches a true rotating field.

Consequently the electromotive .force induced in the phase A, which electromotive force is in quadrature with the impressed electromotive -loI'ce,' increases until a predetermined value is reached, at which the magnet B is sulliciently energized to move contact member (I to open position, thereby breaking the circuit of the starting devices. As long as the motor continues to run magnet D holds contact member 0 in open position; but if the motor is brought to rest for any reasonas, for instance, by a temporary failure of the currentthe contact member 0 will be released and returned automatically to closed position by the counterweight d, so that proper connections are established for starting the motor when it is again supplied with current.

Figs. 3 and 4 show a modified arrangement of the connections of the motor and controlling-magnet. The motorwvindings are shown connected in delta instead of Y, and the phase-splitting devices are shown in sereies with the motor instead of in parallel thereto. The resistance R at starting is connected in series with one motor-terminal and the inductance I in series with a second terminal, both of these terminalsbeing connected to the same terminal of the source. When the motor is up to speed, the resistance R is short-circuited and the inductance I open-circuited,- so that the phase A is connected directly across the line. The controlling-magnet D is connected in shunt to the phase A and the contact member C is arranged to enga e the contacts 0 at starting and contacts 0 when the motor is up to speed and magnet D draws up its armature. At starting the connections are as shown in Fig. 4; but when the contact member 0 bridges the contacts 0 the resistance R is short-circuited and the inductance I open-circuited. With this connection of the motor and controlling-111agnet it will be seen that the magnet is connected across a portion of the motorwinding which is displaced from the portion that is connected across the line when the motor is up to speed by one hundred and twenty degrees instead of by ninety degrees, as in Fig. 1. This phase displacement is sul'licient, however, for proper operation, since the larger component of the electromotive force induced by phase A is in quad rature with the impressed electromotive force, which component is proportional to the cross-field induced in the motor by the secondary currents as the motor comes up to speed.

Other modifications of the connections may be employed, and consequently I do not desire to limit myself to thelparticular con struction and arrangement of parts here cover all modifications which are within the scope of my invention.

\lVhat I claim as new, and desire to secure by Letters Patent of the United States, is-

1. In combination with a single-phase induction-.motor having different connections for starting and for running, a switch adapted to change said connections from starting to running conditions, a magnet-winding controlling said switch, and connections from the motor-winding to said magnet for impressing on said magnet an electromotive force substantially proportional to the cross- I field produced in said motor by the second ary currents.

2. In combination with a single-phase induction-motor having different connections for starting and for running, a switch controlling said connections, and a magnet controlling said switch and connected in shunt to a portion of the motor-winding of different phase from the portion connected across the source of current.

In combination with asingle-phase induction-motor having different connections for starting and for running, a switch adapted to change said connections from starting to running conditions, a magnet-Winding con trolling said switch, and connections for supplying to said magnet-winding an electrornotive force proportional to the electromotive force induced in the motor-winding substantially in quadrature with the impressed electromotive force.

4. In combination with a single-phase induction-motor having a polyphase winding and different connections for starting and for running, a switch controlling said connections, and a magnet-winding controlling said switch and connected in shunt to a phase of the motor-winding not connected to the source of current.

5. In combination with a single-phase induction-motor having a threephase winding and diilercnt connections for starting and for running, a switch controlling said connections, and a magnet-winding controlling said switch and connected between the motor-terminal not connected to the source and a neutral point.

6. In combination with a single-phase induction-motor, a phase-splitting starting device, a switch for breaking the circuit of said' substantialiy proportional to the electroinotive force induced in the motor-Winding in quadrature with the impressed electromotive force, said switch beingarranged to return automatically to closed position when said I nmgnet-winding is denergized.

8. in combination with a single-phase, in; 1 (lllC-tlOH-IIIOtOI, a phase-splitting starting de- I vice, a switch adapted to break the circuit of said device, and a magnet-Winding adapted to open sa d switch and connected in shunt to a portion of the motor-winding of different phase from the portion connected across the source, said switch being arranged to return automatically to closed position when said I 5 magnet-Winding is deenergiz'ed. In Witness whereof]: have hereunto set my hand this 17th day of March, 1906.

SVEN R. BERGMAN Witnesses:

JOHN A. McMANUs, J12, HENRY O. WESTENDARP. 

